Add loading screen, fix tree/foliage collision, jump buffering, and fence rotation

- Loading screen stays visible until all terrain tiles finish streaming;
  character spawns only after terrain is loaded and Z-snapped to ground
- Reduce tree trunk collision bounds (5% of canopy, capped at 5.0) and
  make all small/medium trees, bushes, lily pads, and foliage walkthrough
- Add jump input buffering (150ms) and coyote time (100ms) for responsive jumps
- Fix fence orientation by adding +180° heading rotation
- Increase terrain load radius from 1 to 2 (5x5 tile grid)
- Add hearthstone callback for single-player camera reset

src/rendering/terrain_manager.cpp

@@ -310,7 +310,7 @@ std::unique_ptr<PendingTile> TerrainManager::prepareTile(int x, int y) {
                 p.rotation = glm::vec3(
                     -placement.rotation[2] * 3.14159f / 180.0f,
                     -placement.rotation[0] * 3.14159f / 180.0f,
-                    placement.rotation[1] * 3.14159f / 180.0f
+                    (placement.rotation[1] + 180.0f) * 3.14159f / 180.0f
                 );
                 p.scale = placement.scale / 1024.0f;
                 pending->m2Placements.push_back(p);